**Core Concept**
The combination of ritonavir with lopinavir is based on the principle of pharmacokinetic enhancement, specifically the inhibition of the cytochrome P450 3A4 (CYP3A4) enzyme. This enzyme is responsible for the metabolism of many drugs, including protease inhibitors like lopinavir.

**Why the Correct Answer is Right**
Ritonavir is a potent inhibitor of the CYP3A4 enzyme, which is responsible for the metabolism of lopinavir. By co-administering ritonavir with lopinavir, the metabolism of lopinavir is significantly reduced, leading to increased plasma concentrations and improved antiviral efficacy. This is known as pharmacokinetic boosting. Ritonavir's CYP3A4 inhibition also reduces the metabolism of other protease inhibitors, allowing for lower doses and improved tolerability.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, so we cannot evaluate its correctness.
* **Option B:** This option may refer to a different mechanism, such as synergy or additive effects, but it does not accurately describe the basis of combining ritonavir with lopinavir.
* **Option C:** This option may suggest a different pharmacological interaction, but it does not accurately describe the role of ritonavir in inhibiting CYP3A4 and boosting lopinavir levels.

**Clinical Pearl / High-Yield Fact**
Remember that ritonavir is often used as a pharmacokinetic booster for other protease inhibitors, and its use can significantly impact the dosing and efficacy of these medications.

**Correct Answer: B.**